Altered speech-related cortical network in frontotemporal dementia

Area of Science:

• Neuroscience
• Neurology
• Cognitive Science

Background:

• Healthy subjects (HS) exhibit increased motor-evoked potential (MEP) amplitudes during linguistic tasks, indicating functional connections between speech areas and the primary motor cortex (M1).
• Frontotemporal dementia (FTD) encompasses conditions like non-fluent variant primary progressive aphasia (nfv-PPA) and behavioral variant FTD (bv-FTD), affecting language and behavior.

Purpose of the Study:

• Investigate M1 function using transcranial magnetic stimulation (TMS) in FTD.
• Assess the speech-related cortical network in FTD using neuroimaging techniques.
• Compare M1 excitability and network integrity between FTD subtypes (nfv-PPA, bv-FTD) and HS.

Main Methods:

• TMS was employed to measure M1 excitability during linguistic tasks in 24 FTD patients (15 nfv-PPA, 9 bv-FTD) and 18 HS.
• Diffusion tensor imaging (DTI) assessed white matter (WM) integrity in language-related pathways.
• Voxel-based morphometry (VBM) evaluated grey matter (GM) volume in relevant cortical regions.

Main Results:

• M1 excitability increased in HS during the linguistic task, but not in FTD patients; changes were similar between nfv-PPA and bv-FTD.
• DTI revealed reduced fractional anisotropy in the superior/inferior longitudinal and uncinate fasciculi in FTD patients.
• VBM showed GM volume loss in the left frontal operculum of FTD patients, correlating with linguistic deficits.

Conclusions:

• Converging neurophysiological and neuroimaging evidence demonstrates abnormal speech-related cortical network activation in FTD.
• The findings highlight impaired M1 excitability and structural brain changes in FTD, impacting speech processing.